Personally don't think they are that great. They used to be very good quality a few years ago, but then MAC was sold and they are now not quite so good. You can mix them with gloss etc, or just use them alone. Why not get one in a colour you love and experiment? If you are looking for a budget colour pigment, try Barry M.
You can often find mini pots of them on ebay for much less money (the MAC pots are huge and would take me absolutely years to use up). Barry M dazzle dusts are a good alternative - they don't always have the pigmentation of the MAC ones but you can make them much more intense by layering on top of a primer or over a dark eyshadow.
You can mix them with pretty much anything although they cover themselves by saying you you need to be careful about where you put them (e.g. I think they say you can't use the glitter on your eyes - !)
aquavit, word of advice...Please don't buy them off ebay...
I know they are cheap and allow you to get a variety of colours BUT you honestly have no idea of what it is your are buying.
I used to buy "tester" pigments off ebay against dh's advise (bouthg about 3) and never thought anything more..UNTILL another ebayer contacted me seeing I have bought from the same person who she had, and that what she had was fake, and asked me to check the codes (in fact I had bought a full sized pigment for cheap). She advised me which codes were/weren't genuine. I contacted MAC who confirmed that they weren;t genuine...I was advised that anything is mixed with these products and I since read about people suffering eye damage.
Since, I have NEVER bought makeup from ebay. I have no idea of how genuine it is. I would rather pay full price then risk damage.
I did think of buying pigments and selling samples on myself via ebay till the above happened...also im sure ebay seemed to halt sales of them..
I know its a cheaper alternative but not worth the risk imo..
use a base such as MAC's base and they stick v well and last ages. I have never had an eyeshadow not crease or last long on my eyes..MAC pigments do.
Im sure you can buy a liquid from MAC that you mix with the pigments to make a wet eyeshadow which is more mixable and gives an even better colour and looks WOW...I did have some but ran out..not sure what its called..will try and look x